Git/VCS: Use ctrlc stub for process execution

This ensures that child processes are also terminated.

Required specifically for Git on Windows, when running in cmd directory,
which spawns a child process for usr/bin/git. On this case, if git takes
long to finish and is aborted while running, the main process was killed
as expected, but the child process remained alive.

Task-number: QTCREATORBUG-27567
Change-Id: I40271eb42cfaefd81f2fe5af138254ab0a2c8da8
Reviewed-by: hjk <hjk@qt.io>
Reviewed-by: Christian Stenger <christian.stenger@qt.io>
Reviewed-by: David Schulz <david.schulz@qt.io>
Reviewed-by: Jarek Kobus <jaroslaw.kobus@qt.io>

src/plugins/git/gerrit/gerritplugin.cpp

@@ -119,6 +119,7 @@ FetchContext::FetchContext(const QSharedPointer<GerritChange> &change,
     , m_server(server)
     , m_state(FetchState)
 {
+    m_process.setUseCtrlCStub(true);
     connect(&m_process, &QtcProcess::done, this, &FetchContext::processDone);
     connect(&m_process, &QtcProcess::readyReadStandardError,
             this, &FetchContext::processReadyReadStandardError);